As means for solving the problem of chipping in a dicing process, there is proposed a technology relating to a laser dicing apparatus which launches a laser beam whose condensing point is adjusted to be inside of a wafer, and forms a reformed region due to multi-photon absorption inside the wafer to divide it into individual chips, in place of a conventional cutting by a dicing blade (see, for example, Patent Document 1).
In the laser dicing apparatus as described in Patent Document 1, in order to form a reformed region, which is to be formed inside a wafer, at a fixed depth from the wafer surface, it is necessary to detect the position (height) of the wafer surface and control the position of the condensing point of a laser beam at a high precision.
Therefore, in a conventional laser dicing apparatus, the position of the condensing point of a laser beam is controlled by an autofocus mechanism. To be specific, as illustrated in FIG. 7, a laser beam L1 is radiated from a laser oscillating apparatus 21 toward a wafer. Part of the radiated laser beam L1 becomes incident to the inside of the wafer and is condensed at a certain position (condensing point) forming a reformed region P. The reformed region P formed by the laser irradiation serves as a trigger for the singulation of the wafer into chips. On the other hand, the laser beam L2 reflected by the wafer surface is taken into an optical measuring section 29 via a half mirror 22. The optical measuring section 29 detects an unevenness of the wafer surface based on the received laser beam L2. Then, based on the unevenness detected by the optical measuring section 29, a control section 50 controls a laser oscillating apparatus 21 (precisely, the position of a condensing lens that condenses the laser beam oscillated from the laser oscillating apparatus 21) so that the position of the condensing point of the laser beam in the wafer thickness direction is adjusted in real time for a scanning of the laser beam. Utilizing such an autofocus mechanism makes it possible to perform a high precision dicing that conforms to the unevenness of the wafer surface.
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-175147